doc firmware_sample_firmware_class.c: kmalloc + memset conversion to kzalloc

 Documentation/firmware_class/firmware_sample_firmware_class.c | 5246 -> 5211 (-35 bytes)

Signed-off-by: Mariusz Kozlowski <m.kozlowski@tuxland.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>